Over the years the agricultural and forestry industries have turned increasingly to science to help feed and house the ever increasing human population. Through the development of various herbicides, fertilizers, insecticides and pesticides for terrestial crop and forest uses, man has been able to markedly improve the productivity of the land. The increases in crop and timber production, however, have not been obtained without suffering some adverse consequences.
More particularly, many of the herbicides, fertilizers, insecticides and pesticides that have been developed detrimentally impact the environment in one way or another when used in certain concentrations or under certain conditions. Livestock poisonings, fish kills and other cataclysmic events have resulted. For example, many insecticides such as DDT are particularly stable and resistant to destruction by light and oxidation. With continued use, concentrations of such insecticides may build up in the environment over time to dangerous levels. This may lead to widespread death of wild life and contamination of water supplies deleteriously affecting downstream population centers.
The problem has not gone unnoticed by the government. The Environmental Protection Agency has recently devised new tests specifically designed to collect the data necessary for evaluating the hazard inherent in these types of chemical compounds. One of the studies developed by the government for evaluating the overall environmental impact of, for example, a pesticide is a full degradation study of the pesticide on the surface of a soil sample.
Pesticides may be intentionally applied to the soil surface, remain on the soil surface due to incomplete soil incorporation or reach the soil surface via drift and/or run off from treated areas. Pesticides on the soil surface may undergo photolytic transformation by sunlight. Photolysis is the interaction of a compound with light. More specifically, light energy is transferred to the chemical bonds of the compound, either directly or indirectly through another compound. This energy serves to break the bonds and the original compound is transformed to another compound or compounds known as photoproducts. The purpose of the soil photolysis studies is to provide data on pesticide degradation rates and on the formation and decline of photoproducts on soil surfaces. It is important to complete soil studies since a photoproduct formed on soil may react with the soil organic matter or be metabolized by soil microorganisms, thus producing possibly unique degradation products. In order to determine potential hazards of the pesticide the rates of photolysis and half lives of the parent pesticide and its photodegradates must be studied and determined in order to establish the importance of the transformation process and the persistence characteristics of photoproducts that may be formed.
Exacting test procedures have been developed to accurately determine the rates of soil surface photolysis of pesticides and to identify photoproducts and rates of formation and decline of these products. Procedures are standardized so that results of various studies, even when conducted by different groups, may be effectively compared.
Preferably, the test samples are exposed to natural sunlight conditions. Thus, the environmental chamber for containing the test samples must be supported in a way so as not to block the passage of light to the samples. In addition, the environmental chamber must include an optically pure wall allowing the passage of natural sunlight to the test samples without filtering any of the radiation.
Of course, the passage of light into the environmental chamber tends to heat the chamber. In fact, the soil surface holding the test samples within the environmental chamber could reach temperatures nearly twice that experienced in the actual environment where the particular pesticide would be sprayed. These higher temperatures could cause reactions and the production of unique photoproducts that would not occur in the lower soil temperatures of the actual environment. Because of this, the apparatus should also include a temperature control mechanism for maintaining the temperature of the test samples and soil within a desired range approaching that of the actual environment in which the pesticide is to be used.
A further concern relates to the need to minimize the loss of test sample through volatilization. In order to accurately determine the photolysis rate of the test sample, the volatiles emitted by the test sample should be collected. Further, these volatile photoproducts should be identified if emitted in any appreciable level. Thus, in order to carry out this procedure, the environmental chamber must be sealed and provide some means for collecting the emitted volatiles. In addition, it is preferred that at least a portion of the test sample and soil be available for convenient recovery from the environmental chamber to allow periodic testing at specific time intervals. This will allow the identification of degradation products that may, be produced by the reaction of photoproducts with the soil organic matter or the metabolization of those products by soil microorganisms.
To date, the present inventors are unaware of any apparatus that has been developed that may be used to effectively meet the criteria discussed above. A need, therefore, exists for a simple and effective apparatus that may be utilized in performing soil photolysis studies.